The liquid crystal display device is a space-saving image display device with low power consumption, and the use thereof is increasing every year. In addition to the market, for example, for TVs and the like where high-quality images are required, there is higher need for thinning as markets for so-called mobile use, such as mobile phones and tablet PCs are expanded.
The basic configuration of a liquid crystal display device is that polarizing plates are disposed on both sides of a liquid crystal cell. The polarizing plate serves to transmit only a light of a plane of polarization in a specific direction, and the performance of the liquid crystal display device greatly depends on the performance of the polarizing plate. The polarizing plate generally has a configuration including a polarizer composed of a polyvinyl alcohol film and the like, on which iodine or a dye is adsorbed and oriented, and transparent protective films bonded to inner and outer sides of the polarizer. A cellulose acylate-based polarizing plate protective film, typified by cellulose acetate, has high transparency and readily secures adhesion to polyvinyl alcohol used in the polarizer, and thus, has been widely used as a polarizing plate protective film.
As the liquid crystal display devices become thinner, gaps between a liquid crystal panel and a backlight unit become narrower, and thus, the level required for dimensional stability of each member has been further rigorous. Even for the polarizing plate, it is required that the polarizing plate itself becomes thinner and curling or change in dimension of the polarizing plate is decreased. In particular, the contraction of the polarizing plate under high temperature and high humidity environments is responsible for warping or distortion of a panel, which causes the display to become uneven, and thus, the improvement thereof has been strongly required.
To solve the problem, Japanese Patent Application Laid-Open No. 2007-47536 and International Publication WO 0717565 disclose a method for reducing display unevenness by thinning a polarizing film and a polarizing plate protective film to decrease stress in a liquid crystal panel caused by contraction of the entire polarizing plate.